Superconductivity in cuprates emerges out of a complex normal state that hosts density waves, pseudogap physics, and strange metal properties. Here, we access this normal state by synchronizing free-electron laser x-rays with high-magnetic-field pulses up to 44 T. We observe a linear increase in charge order amplitude and correlation length that persists far above the vortex melting transition. This behavior is incompatible with standard phase competition between charge order and superconductivity. By means of conventional hard x-ray diffraction and magnetostriction, we show that applied fields also enhance monoclinic lattice distortions. However, this magnetoelastic response is weaker and an epiphenomenon of the stripe order enhancement. Combined with recent observations of field-linear spin freezing, our results point to a direct coupling between magnetic field and the spin component of stripe order in the high-field normal state – a mechanism independent of superconductivity suppression that has so far remained hidden from scattering probes.

Nanoscale miniaturization has revolutionized the field of spintronics by enabling exponential growth in areal bit density. A similar leap is also expected in device speeds through successfully harnessing femtosecond magnetization dynamics. However, combining this with the miniaturization of realistic devices is challenging. To address this, we studied the effect of dimensional confinement on the femtosecond demagnetization of Fe. By gradually increasing the level of confinement while keeping excitation conditions constant, we found that Fe layers thinner than 10 nm exhibit enlarged demagnetization amplitudes, reaching a ∼75% increase at 2 nm. By combining ultrafast experiments sensitive to the spins, the charge carriers, and the phonons, we establish that this finite-size effect is magnetic in origin and is not phonon-driven. With the support of ab-initio calculations and atomistic spin dynamics simulations, we identify the enhancement effect as due to local weakening of spin order at the Fe's interface, which becomes significant upon increased confinement.

Local material inhomogeneities can strongly influence magnetization dynamics and macroscopic magnetic properties, yet detecting such defects from magnetic imaging data remains challenging when thermal fluctuations and experimental noise obscure static contrast. Here, we investigate defect detection in strongly fluctuating magnetization regimes where signatures of inhomogeneities largely average out in time-resolved measurements. Using finite-temperature micromagnetic simulations with randomly distributed defects and material parameters representative of Ni80Fe20, we compute per-pixel temporal mean, temporal standard deviation, and latent entropy and use them as inputs for U-Net-based semantic segmentation models. We find that the most effective descriptor depends on the noise level and, importantly, that robust detection requires training data that reflect the expected noise statistics. These results provide practical guidance for designing noise-robust defect-detection workflows in magnetic imaging.

Unraveling the mechanism behind bulk perpendicular magnetic anisotropy (PMA) in amorphous rare earth-transition metal films has proven challenging. This is largely due to the inherent complexity of the amorphous structure and the entangled potential origins arising from microstructure and atomic structure factors. Here, we present an approach wherein the magneto-electric effect is harnessed to induce 90° switching of bulk PMA in Tb-Co films to in-plane directions by applying voltages of only -1.2 V. This manipulation is achieved by voltage-driven insertion of hydrogen atoms into interstitial sites between Tb and Co atoms, which serves as a perturbation to the local atomic structure. Using angle-dependent X-ray magnetic circular dichroism, we find that the anisotropy switching originates from the distortion of the crystal field around Tb, which reorients the alignment of Tb orbital moments. Initially aligned along Tb-Co bonding directions, the easy magnetization axis undergoes reorientation and switches by 90°, as substantiated by ab initio calculations. Our study not only concludes the atomic origin of Tb-Co atom bonding configuration in shaping bulk PMA but also establishes the groundwork for electrically programmable ferrimagnetic spintronics, such as controlling domain wall motion and programming artificial spin textures.

At equiatomic composition, FeV alloys form metastable phases such as the B2 phase or a short-range ordered phase in favor of the equilibrium 6 phase. In this regime, structural, magnetic, and vibrational properties are strongly influenced by atomic disorder. For thermally co-evaporated Fe1-xVx thin-films, the non-equilibrium phase diagram is explored and the short-range ordered phase that forms at equiatomic compositions is compared to its base-centered cubic counterpart. The results indicate that within the short-range ordered thin-films, the structural disorder is accompanied by an increase in chemical order, i.e. Fe and V atoms are their respective preferential nearest neighbors. These observations are important for a better understanding of recrystallization in nonmagnetic, short-range ordered templates, in which crystallization can be selectively triggered.

Nanocrystalline (similar to 10 nm) singe-fcc CoCrFeNiGax (x = 0.5, 1.0) high entropy alloy (HEA) particles with excellent structural and compositional homogeneity were prepared from elemental powders using single-step, short-term (190 min) high energy ball milling (HEBM) at room temperature (RT). Both HEA powders exhibit paramagnetic behaviour at RT with a small ferromagnetic contribution at low fields (saturation magnetization M-s= 4.5 - 7.5 Am-2/kg; average Curie temperature T-c = 130 K - 150 K). They are thermally stable up to 1295 K-1305 K despite the low melting temperature of Ga (302.9 K). Heat treatment up to 1000 K enhances M-s to 59.9 Am-2/kg and T-c to 740 K for the CoCrFeNiGa HEA powder due to an irreversible fcc -> bcc structural transformation, whereas the magnetic properties of CoCrFeNiGa0.5 do not show this enhancement. In-situ TEM heating reveals nanosized sigma-phase Cr-rich precipitates (< 50 nm) at 875 K only for the CoCrFeNiGa HEA powder. Spark plasma sintering (SPS) of powders produces homogeneous nanocrystalline bulk HEAs. SPS at 1073 K of the CoCrFeNiGa0.5 powder increased the crystallinity of the fcc phase. Three-dimensional local compositional mapping at atomic resolution by atom probe tomography indicates a homogeneous distribution of all elements. Bulk HEAs exhibit similar magnetic behavior as heat-treated HEA powders. Combining HEBM and SPS yields homogeneous bulk HEAs with low-melting Ga and enhanced structural, composition, and thermal stability, as well as improved magnetic properties (M-s = 55Am(2)/kg and T-c = 750 K), which is 45% and 47 K higher, respectively, compared to conventional melting approaches.

Magnetic cooling has the potential to replace conventional gas compression refrigeration. Materials such as La(Fe,Si)$_{13}$ exhibit a sizeable first-order magnetocaloric effect, and it is possible to tailor the phase transition towards room temperature by Mn-H-doping, resulting in a large temperature range for operation. Within this work, we discuss variations of the electronic and lattice structure in La(Fe,Si)$_{13}$ with increasing Mn content utilizing X-ray magnetic circular dichroism (XMCD) and extended X-ray absorption fine structure spectroscopy (EXAFS). While XMCD shows a decrease of the magnetic polarization at the Fe K edge, low-temperature EXAFS measurements indicate increased positional disorder in the La environment that is otherwise absent for Fe and Mn. First-principles calculations link the positional disorder to an enlarged Mn-Si distance -- explaining the increased positional disorder in the La surrounding.

Permanent magnets draw their properties from a complex interplay of chemical composition and phase, each with their associated intrinsic magnetic properties. Gaining an understanding of these interactions is the key to deciphering the origins of a permanent magnets’ magnetic performance and facilitate the engineering of much improved-performing magnets. Here, we use advanced multiscale microscopy and microanalysis on a bulk Sm2(Co,Fe,Cu,Zr)17 pinning-type high-performance magnet with outstanding thermal and chemical stability. Comparison of the microstructure in regions of different composition, we demonstrate that the pinning of magnetic domains, imaged by nanoscale magnetic induction mapping, is controlled by the composition and atomic arrangement of copper. This is confirmed by micromagnetic simulations. Contrary to the belief that grain boundaries are “weak links” in magnetic materials, we demonstrate grain boundaries undergo magnetization reversal at relatively low fields (0.1-0.3 T), but this remains confined to these regions and does not significantly impact the magnet’s coercivity. Our results showcase that it is the optimal microstructure within the grain itself that is crucial for achieving the desired magnetic properties. Rare-earth permanent magnets are engineered with a complex microstructure of composition and phase, grains and grain boundaries, and it is this complex structure which leads to the magnetic performance. Here, Giron and coauthors, through thorough microstructural analysis, demonstrate that the grain microstructure, not grain boundaries, are primarily responsible for optimal magnetic properties.

We present a novel instrument designed for advanced magnetic study, installed at the ID12 beamline of the European Synchrotron Radiation Facility in Grenoble, France. This instrument offers the unique capability to simultaneously measure element-specific microscopic and macroscopic properties related to the magnetic, electronic and structural characteristics of materials. In addition to X-ray absorption, X-ray magnetic circular dichroism alongside X-ray diffraction patterns, the macroscopic magnetization, volume changes, caloric properties and electrical resistivity of magnetic materials could be measured strictly under the same experimental conditions as a function of both magnetic field (up to ±7 T) and temperature (ranging from 2.05 K to 325 K). To demonstrate the capability of this new instrument, we present two case studies highlighting its performance in investigating first-order magneto-structural phase transitions, namely in DyCo2 and FeRh alloys.

Among the magnetocaloric materials featuring first-order phase transitions (FOPT), FeRh is considered as a reference system to study the FOPT because it is a "simple" binary system with a CsCl structure exhibiting a large adiabatic temperature change. Recently, ab initio theory predicted that changes in the Fe/Rh stoichiometry in the vicinity of equiatomic composition strongly influence the FOPT characteristics. However, this theoretical prediction was not clearly verified experimentally. Here, we investigated the composition dependence of the transitional hysteresis in FeRh. It is shown that a Fe excess of only 1 at. % induces a ferromagnetic state in the whole temperature range (from 5 K up to Tc) for a minor portion of the sample (≈10%), while 5 at. % is enough to completely eliminate the FOPT. Element-specific X-ray magnetic circular dichroism (XMCD) measurements suggest that this ferromagnetic contribution arises from residual FeRh ferromagnetic regions. We attribute the formation of such domains to Fe antisite defects, as Mössbauer spectroscopy demonstrates the presence of Fe atoms located at the 1b (Rh) sites in the CsCl-type structure. As a consequence, compared with the equiatomic composition, the slightly Fe-rich sample exhibits completely different FOPT properties, influencing the magnetocaloric performances. Thus, our study sheds light on the origin of the remarkable stoichiometric sensitivity of the FOPT behavior in FeRh. These insights have broader implications for understanding FOPT dynamics and the role of residual ferromagnetic domains.

Photo-doped states in strongly correlated charge transfer insulators are characterized by $d$-$d$ and $d$-$p$ interactions and the resulting intertwined dynamics of charge excitations and local multiplets. Here we use femtosecond x-ray absorption spectroscopy in combination with dynamical mean-field theory to disentangle these contributions in NiO. Upon resonant optical excitation across the charge transfer gap, the Ni $L_3$ and O $K$ absorption edges red-shift for $>10$ ps, which is explained by a simultaneous Hartree shift and a renormalization of the local interactions. Furthermore, below the Ni $L_3$ edge an additional signature is identified for $<1$ ps, which reflects a transient nonthermal population of local many-body multiplets. Overall, the photo-doped state differs significantly from a chemically doped state. Our results demonstrate the ability to reveal excitation pathways in correlated materials by x-ray spectroscopies, which is relevant for ultrafast materials design.

The rise of Fe magnetic moment, changes in Al electronic structure and a variation of Al magnetic polarization in thin films of transition metal aluminide Fe60Al40 have been probed through the order-disorder phase transition by soft x-ray absorption spectroscopy and x-ray resonant magnetic reflectivity in the extreme ultraviolet regime. In a course of the transition induced by 20 keV Ne+ irradiation with low fluences (similar to 10(14) ions cm(-2)), x-ray magnetic circular dichroism spectra taken at the Fe L-2,L-3 absorption edges at room and low temperatures revealed a pronounced increase of Fe 3d states spin-polarization. X-ray resonant magnetic reflectivity applied to the Al L-2,L-3 and Fe M-2,M-3 edges allowed to detect the magnetic polarization of Al atoms in the films. The changes in Al electronic structure have been seen by alteration of Al K edge x-ray absorption near edge structure. A difference in anisotropy fields for films before and after irradiation has been observed by element-specific hysteresis loops recorded at low temperatures in absorption and reflection geometries at the Fe L-2,L-3 and M-2,M-3 edges, respectively. An attempt to reduce the top oxide layer by an inductively coupled hydrogen plasma has shown a possibility to recover the chemically ordered phase.

The tailoring of spin-crossover films has made significant progress over the past decade, mostly motivated by the prospect in technological applications. In contrast to spin-crossover complexes in solution, the investigation of the ultrafast switching in spin-crossover films has remained scarce. Combining the progress in molecule synthesis and film growth with the opportunities at X-ray free-electron lasers, we study the photoinduced spin-state switching dynamics of a molecular film at room temperature. The subpicosecond switching from the S = 0 low-spin ground state to the S = 2 high-spin state is monitored by analyzing the transient evolution of the Fe L3 X-ray absorption edge fine structure, i.e. element-specifically at the switching center of the Fe(II) complex. Our measurements show the involvement of an intermediate state in the switching. At large excitation fluences, the fraction of high-spin molecules saturates at ≈50%, which is likely due to molecule-molecule interaction within the film.

Time-resolved X-ray absorption spectroscopy (tr-XAS) has been shown to be a versatile measurement technique for investigating non-equilibrium dynamics. Novel X-ray free electron laser (XFEL) facilities like the European XFEL offer increased repetition rates for stroboscopic XAS experiments through a burst operation mode, which enables measurements with up to 4.5 MHz. These higher repetition rates lead to higher data acquisition rates but can also introduce long-lived excitations that persist and thus build up during each burst. Here, we report on such long-lived effects in Ni and NiO thin film samples that were measured at the European XFEL. We disentangle the long-lived excitations from the initial pump-induced change and perform a detailed modelling-based analysis of how they modify transient X-ray spectra. As a result, we link the long-lived effects in Ni to a local temperature increase, as well as the effects in NiO to excited charge carrier trapping through polaron formation. In addition, we present possible correction methods, as well as discuss ways in which the effects of these long-lived excitations could be minimized for future time-resolved X-ray absorption spectroscopy measurements.

The transition toward a carbon-neutral society based on renewable energies goes hand in hand with the availability of energy-efficient technologies. Magnetocaloric cooling is a very promising refrigeration technology to fulfill this role regarding cryogenic gas liquefaction. However, the current reliance on highly resource critical, heavy rare-earth-based compounds as magnetocaloric material makes global usage unsustainable. Here, we aim to mitigate this limitation through the utilization of a multicaloric cooling concept, which uses the external stimuli of isotropic pressure and magnetic field to tailor and induce magnetostructural phase transitions associated with large caloric effects. In this study, La0.7Ce0.3Fe11.6Si1.4 is used as a nontoxic, low-cost, low-criticality multiferroic material to explore the potential, challenges, and peculiarities of multicaloric cryocooling, achieving maximum isothermal entropy changes up to -28 J (kg K)(-1) in the temperature range from 190 K down to 30 K. Thus, the multicaloric cooling approach offers an additional degree of freedom to tailor the phase transition properties and may lead to energy-efficient and environmentally friendly gas liquefaction based on designed-for-purpose, noncritical multiferroic materials.

Permanent magnets draw their properties from a complex interplay, across multiple length scales, of the composition and distribution of their constituting phases, that act as building blocks, each with their associated intrinsic properties 1. Gaining a fundamental understanding of these interactions is hence key to decipher the origins of their magnetic performance2 and facilitate the engineering of better-performing magnets, through unlocking the design of the “perfect defects” for ultimate pinning of magnetic domains3. Here, we deployed advanced multiscale microscopy and microanalysis on a bulk Sm2(CoFeCuZr)17 pinning-type high-performance magnet with outstanding thermal and chemical stability 4. Making use of regions with different chemical compositions, we showcase how both a change in the composition and distribution of copper, along with the atomic arrangements enforce the pinning of magnetic domains, as imaged by nanoscale magnetic induction mapping. Micromagnetic simulations bridge the scales to provide an understanding of how these peculiarities of micro- and nanostructure change the hard magnetic behaviour of Sm2(CoFeCuZr)17 magnets. Unveiling the origins of the reduced coercivity allows us to propose an atomic-scale defect and chemistry manipulation strategy to define ways toward future hard magnets.

The shell-ferromagnetic effect originates from the segregation process in off-stoichiometric Ni–Mn-based Heusler.

In this contribution we will present two new instruments implemented at the beamline ID12 of the European Synchrotron Radiation Facility (ESRF) in the framework of the ULMAG – "Ultimate MAGnetic characterization" collaborative project. These instruments offer the ESRF users a unique possibility to measure under strictly the same experimental conditions the element-specific X-ray absorption spectroscopy (XAS)/X-ray magnetic circular dichroism (XMCD), and X-Ray Diffraction (XRD) simultaneously with various macroscopic properties (magnetization, magnetostriction, magnetocaloric, magnetoresistance), as a function of magnetic field (up to 17 T) and temperature (5-325 K). To demonstrate the potential and features of these scientific instruments, we will present two case studies: (1) FeRh, which has a first-order anti-ferromagnetic to ferromagnetic transition around room temperature and (2) HoCo2, which exhibits a first-order ferrimagnetic to paramagnetic transition. These two cases demonstrate new horizons for studying the physics of magnetic materials, where the interplay between the magnetic, structural, and electronic subsystems of the solid is essential.

Free-electron lasers provide bright, ultrashort, and monochromatic x-ray pulses, enabling novel spectroscopic measurements not only with femtosecond temporal resolution: The high fluence of their x-ray pulses can also easily enter the regime of the non-linear x-ray–matter interaction. Entering this regime necessitates a rigorous analysis and reliable prediction of the relevant non-linear processes for future experiment designs. Here, we show non-linear changes in the L3-edge absorption of metallic nickel thin films, measured with fluences up to 60 J/cm2. We present a simple but predictive rate model that quantitatively describes spectral changes based on the evolution of electronic populations within the pulse duration. Despite its simplicity, the model reaches good agreement with experimental results over more than three orders of magnitude in fluence, while providing a straightforward understanding of the interplay of physical processes driving the non-linear changes. Our findings provide important insights for the design and evaluation of future high-fluence free-electron laser experiments and contribute to the understanding of non-linear electron dynamics in x-ray absorption processes in solids at the femtosecond timescale.